Verified maintainer script warning on all releases:

root@bb-proposed:~# grep AuthorizedKeysCommand /etc/ssh/sshd_config
AuthorizedKeysCommand /bin/false
#AuthorizedKeysCommandUser nobody
root@bb-proposed:~# apt install -qq ec2-instance-connect
The following package was automatically installed and is no longer required:
  libfreetype6
Use 'apt autoremove' to remove it.
The following NEW packages will be installed:
  ec2-instance-connect
0 upgraded, 1 newly installed, 0 to remove and 76 not upgraded.
Need to get 12.6 kB of archives.
After this operation, 57.3 kB of additional disk space will be used.
Selecting previously unselected package ec2-instance-connect.
(Reading database ... 36957 files and directories currently installed.)
Preparing to unpack .../ec2-instance-connect_1.1.12+dfsg1-0ubuntu3~18.04.0_all.deb ...
Created system user ec2-instance-connect
Unpacking ec2-instance-connect (1.1.12+dfsg1-0ubuntu3~18.04.0) ...
Setting up ec2-instance-connect (1.1.12+dfsg1-0ubuntu3~18.04.0) ...
Created symlink /etc/systemd/system/multi-user.target.wants/ec2-instance-connect.service → /lib/systemd/system/ec2-
instance-connect.service.
Job for ec2-instance-connect.service failed because the control process exited with error code.
See "systemctl status ec2-instance-connect.service" and "journalctl -xe" for details.
ERROR: Not restarting ssh because /etc/ssh/sshd_config already sets
ERROR: AuthorizedKeysCommand*, which is also set by
ERROR: /lib/systemd/system/ssh.service.d/ec2-instance-connect.conf.
Please restart ssh manually if the configuration is correct.
root@bb-proposed:~#

root@ee-proposed:~# grep AuthorizedKeysCommand /etc/ssh/sshd_config
AuthorizedKeysCommand /bin/false
#AuthorizedKeysCommandUser nobody
root@ee-proposed:~# apt install -qq ec2-instance-connect
The following packages were automatically installed and are no longer required:
  command-not-found-data libdumbnet1 libidn11 libip4tc0 libip6tc0 multiarch-support
Use 'apt autoremove' to remove them.
The following NEW packages will be installed:
  ec2-instance-connect
0 upgraded, 1 newly installed, 0 to remove and 34 not upgraded.
Need to get 12.6 kB of archives.
After this operation, 57.3 kB of additional disk space will be used.
Selecting previously unselected package ec2-instance-connect.
(Reading database ... 32593 files and directories currently installed.)
Preparing to unpack .../ec2-instance-connect_1.1.12+dfsg1-0ubuntu3~19.10.0_all.deb ...
Created system user ec2-instance-connect
Unpacking ec2-instance-connect (1.1.12+dfsg1-0ubuntu3~19.10.0) ...
Setting up ec2-instance-connect (1.1.12+dfsg1-0ubuntu3~19.10.0) ...
Created symlink /etc/systemd/system/multi-user.target.wants/ec2-instance-connect.service → /lib/systemd/system/ec2-
instance-connect.service.
Job for ec2-instance-connect.service failed because the control process exited with error code.
See "systemctl status ec2-instance-connect.service" and "journalctl -xe" for details.
ERROR: Not restarting ssh because /etc/ssh/sshd_config already sets
ERROR: AuthorizedKeysCommand*, which is also set by
ERROR: /lib/systemd/system/ssh.service.d/ec2-instance-connect.conf.
Please restart ssh manually if the configuration is correct.
root@ee-proposed:~#

root@x-proposed:~# grep AuthorizedKeysCommand /etc/ssh/sshd_config
AuthorizedKeysCommand /bin/false
root@x-proposed:~# apt install -qq ec2-instance-connect
The following package was automatically installed and is no longer required:
  libfreetype6
Use 'apt autoremove' to remove it.
The following NEW packages will be installed:
  ec2-instance-connect
0 upgraded, 1 newly installed, 0 to remove and 56 not upgraded.
Need to get 12.5 kB of archives.
After this operation, 56.3 kB of additional disk space will be used.
Selecting previously unselected package ec2-instance-connect.
(Reading database ... 25741 files and directories currently installed.)
Preparing to unpack .../ec2-instance-connect_1.1.12+dfsg1-0ubuntu3~16.04.0_all.deb ...
Created system user ec2-instance-connect
Unpacking ec2-instance-connect (1.1.12+dfsg1-0ubuntu3~16.04.0) ...
Setting up ec2-instance-connect (1.1.12+dfsg1-0ubuntu3~16.04.0) ...
Job for ec2-instance-connect.service failed because the control process exited with error code. See "systemctl stat
us ec2-instance-connect.service" and "journalctl -xe" for details.
ec2-instance-connect.service couldn't start.
ERROR: Not restarting ssh because /etc/ssh/sshd_config already sets
ERROR: AuthorizedKeysCommand*, which is also set by
ERROR: /lib/systemd/system/ssh.service.d/ec2-instance-connect.conf.
Please restart ssh manually if the configuration is correct.
root@x-proposed:~#